Color television picture tube



Feb. 5, 1963 J. GIUFFRIDA 3,076,910

COLOR TELEVISION PICTURE TUBE Filed Sept. 16, 1955 3 Sheets-Sheet l FIG.1

PF/QF x94 7 INVENTOR. Joseph Giuffridu ATTORNEY Feb. 5, 1963 J. GIUFFRIDA COLOR TELEVISION PICTURE TUBE 3 Sheets-Sheet 2 Filed Sept. 16, 1955 PA /0 AFT FIG.3

INVENTOR Joseph Giuffridu ATTORNEY Feb. 5, 1963 J. GIUFFRIDA 3,076,910

COLOR TELEVISION PICTURE TUBE Filed Sept. 16, 1955 3 Sheets-Sheet 3 INVENTOR. Joseph Giuffridu ATTORNEY titates Patent 3,d76,9ih QQLOR TELEVKSIION PXQTURE TUBE .l'esenh Gish-ride, heebody, Mass, assignor to Columbia Broadcasting System, End, a corporation of New York,

doing business under the name of Chii-Hytron, a D1- vision of Columbia Broadcasting System, inc, Danvers, Mass.

Filed Sept. 16, W55, Ser. No. 534,824 it) Claims. (Cl. 313-92} The invention relates in general to color television picture tubes and in particular to multiple electron beam aperture mask types of color picture tubes.

At this time the most promising version of color television picture tube is that which utilizes multiple electron beams, an aperture mask and a phosphor dot screen. The phosphor dots are symmetrically arrayed in groups of three color-generating types over the faceplate of the tube. Behind them is an aperture mask which has circular apertures symmetrically formed in its surface. The phosphor groups are so oriented relative to the mask that one aperture of the mask lies directly behind each group of phosphors. Any one electron beam can see only dots of one type of phosphor through the apertures of the mask. Thus, in these color tubes we have a red beam which impinges only on red phosphor dots, a green beam which impinges only on green phosphor dots, and a blue beam which impinges only on blue phosphor dots.

As noted above, the phosphor dot screen is formed directly on the faceplate of the tube and hence has a spherical configuration. The aperture mask has a matching spherical contour in accordance with the teaching of Fyler and lowe, United States Patent No. 2,690,518, assigned to the same assignee as the present application. Although the recently abandoned flat stressed mask tube had a far greater need for dynamic convergence, even the curved screen-curved mask type tube of the cited patent requires some dynamic convergence. By way of explanation, the term dynamic convergence means that the electron beams are brought to a desired cross-over point at all times as they are scanned over the spherical mask and screen. This cross-over point is, of course, preferably at the apertures of the mask.

in actual practice, there are three electron guns dispose symmetrically in the neck of the tube in a circle. The center of the circle coincides with the longitudinal axis of the tube, and each gun is inclined toward that axis causing the electron beams to be directed inwardly toward each other. Tl original converging paths of the beams, if unmodified, would result in a cross-over point substantially at an aperture of the mask on the tube axis. in the absence of dynamic convergence, if the beams are defiected, it is clear that the cross-over points will remain the same distance from the d-eiection plane. This spherical locus of cross-over points does not coincide with the spherical aperture mask, because practical tube viewing considerations demand a faceplate and a mask of matching curvature having a radius of curvature greater than the distance from the deflection plane to the cross-over points.

Furthermore, there are inevitably aberrations introduced by yoke field non-uniformity which serve to change the crossover points as the beams are deflected. Finally, even under ideal conditions, only a first order focus can be achieved anywhere but on the axis of the tube.

To provide feasible dynamic convergence, the practice has been to reduce the initial convergence angle by providing varying magnetic deflection at the so-called convergence plane. The magnetic deflection is synchronized with the scanning currents and is designed to reduce the convergence angle of the electron beams in proportion to the instantaneous angular displacement of the beams from ice the axis. At the axis itself, of course, the amount of displacement of the beams is zero.

In tubes made in accordance with the teaching of the application of Perry and Rowe, Serial No. 387,192, filed October 20, 1953, and assigned to the same assignee as the present case, the phosphor dots are formed photographically by exposure through the aperture mask of photosensitized phosphor. In accordance with that application, a light source for forming the dots is placed at positions corresponding to positions in the deflection plane of a finished tube through which the three electron beams will pass. In other words, the light source for forming the phosphor dots is placed at each of the apparent sources of electrons in a finished tube.

Reduction of the initial convergence angle in the dynamic convergence plane causes the three beams to pass through the deflection plane at points further from the axis than the points corresponding to the positions of the light source. It can be easily shown that this results in a color tube in which the center of the electron beam is shifted away from the center of the phosphor dot on which it is designed to impinge toward an adjacent dot of a different color-generating type. The amount of shift is proportional to deflection causing the extreme corners i of a rectangular tube to be most affected.

Although the shift is not of sufficient magnitude to cause severe color purity trouble in most tubes of sizes currently being produced, it has been recognized as a potential source of difficulty. Standards of quality in a device as important to color television as the picture tube demanded that this marginal condition be eliminated.

The only curative measure applied prior to the present invention has been the use of a graded hole mask. in

this device, the mask was provided with apertures which were gradually reduced in size as their distance from the center increased. The phosphor dots were uniformly as large as the center dots. As a result, a beam was prevented from either impinging beyond or on the peripheries of the phosphor dots simply because it was reduced in size as it came through the reduced aperture. This expedient maintained color purity quite well, but at a cost in light output that rendered it useless as a practical solution to the color purity problem. Over and above the loss in light output due to the beam-slimming effect, the graded hole mask itself was expensive to produce and impractical to use in photographic deposition techniques of fabricating the tubes.

Therefore, it is a primary object of this invention to provide a color television picture tube having uniform color purity and uniform high light output over its entire screen area.

It is a further object of this invention to provide an inexpensive solution to the problem of maintaining dynamic convergence without loss of other desirable characteristics in color television picture tubes.

It is a still further object of this invention to simplify the construction of color television picture tubes without deleteriously affecting their performance.

it is another object of this invention to provide a novel convergence structure for effecting dynamic convergence.

It is still another object of this invention to provide a method of color tube fabrication which compensates for electron beam shift due to dynamic convergence.

In general, the present invention consists: in alterna tive means and methods for retaining at least: three quality features formerly considered to be mutually exclusive in color television picture tubes. These features are color purity, high light output and adequate dynamic convergence. One of the means embodying the present invention is a double convergence plane in the tube rather than the present single plane. The second convergence plane may include internal sets of pole pieces and eX- smears ternal coils and cores for each gun. By this arrangement, the first convergence plane may be used to increase the initial convergence angle and the second convergence plane may be used to decrease the convergence angle and provide beams almost parallel to the tube axis. Proper adjustments then permit the beams to pass through the deflection plane at points corresponding identically to the points of apparent source of the electrons.

A preferred method of practicing the present invention in the fabrication of color television picture tubes by the photographic process is to move the light source to positions other than those normally used in the deposition of the phosphor dots. These new positions would be on a circle of larger diameter than that normally used. In fact, the change in position would cons-titute only a. small radially outward movement in each case. The amount of movement would be determined by the size of tube and screen as. will be, explained in detail hereinafter. The points of formation of phosphor dots resulting from such relocation are shifted slightly radially outward with respect tov the center of each tricolor phosphor dot triangle resulting in slightly more eccentricity of beam to phosphor dot near the center of the tube but much less. eccentricity at the edges of the screen. Since there is ample provision for variation in the center area, due to substantially perfect beam landing at that point, and a maximum error at the edge of the screen, the compromise is justifiable in producing a slight error at the center of the screen which does not effect color purity in order to. decrease the error found at the edges of the screen thereby improving color purity in that portion of the screen. For a better understanding of the invention together with other objects, features and advantages, reference should be made to the following description which is to be read in connection with the drawings in which:

FIG. 1 is a schematic representation of a rectangular screen showing beam shift with dynamic convergence, applied as taught in the prior art;

FIG. 2 is a schematic diagram of the conditions obtaining in prior art tubes;

FIG. 3 is a schematic diagram of the conditions obtaining in a tube made in accordance with one embodiment of the present invention;

FIG. 4 is a perspective view of a color television picture tube partly cut away to show details of the construction of the electron gun and convergence devices; and

FIG. 5 is a schematic idealized view of apparatus for projecting the image of an aperture mask to locate phosphor dots on the screen of a picture tube.

Referring particularly to FIG. 1, there is shown a faceplate 12 of a prior art color television picture tube. Considering the position of the observer to be within the tube looking toward the faceplate, central phosphor d ts 13, 14 and 15 are visible and are represented by the larger circles. The smaller circles 16, 17 and 18 represent cross-sections of the electron beams impinging upon the phosphor dots. Because phosphor dots 13, 14 and 15 are in or very near the central screen area, as was explained above, even though dynamic convergence is used, its effect is zero on the central beams and the crosssections of those central beams are substantially concen tric with the phosphor dots.

In the case of screen edge areas wherein phosphor dots 22, 23 and 24 are typical, the passage of the electron beams through the deflection plane at points not coincident with points corresponding to light source locations causes the indicated shifts. The cross-section of beams 25, 2 6 and 27 are shown in their relationship to the phosphor dots 22, 23 and 24. As may be seen in the drawing, the shift in each case at screen edges is considerable and leaves little or no margin for error. The slightest additional beam shift caused by any one of numerqus possible factors will result in loss of edge purity.

FIG. 2 is an exaggerated view of the geometry of the beam shift illustrated in FIG. 1. A gun 31 is shown at the neck end and a phosphor screen 32 and aperture mask 33 at the viewing end of a tube. Gun 31 may be any one of the three guns, the tube being so oriented that its longitudinal axis and that of the gun in question lie in a plane.

Neglecting the influence of external stray magnetic fields, if the tube is perfectly aligned, the undeflected beam from gun 31 will pass through the aperture mask on the axis OF of the tube. The path of the undeflected beam is identified as. line DF. This result is had simply by reason of the physical tilt or inclination toward the tube axis of gun 31. No dynamic convergence is applied at the convergence plane 34 because, as previously noted, dynamic convergence is made a function of beam deflection and is zero when deflection is zero as it is at the deflection plane 35.

In the case of a deflected beam, however, the situation is quite different. Recognition of the need for dynamic convergence to. match loci of beam crossover points to the spherical contour of the mask has led to general use of a system for reducing the initial convergence. angle as a function of deflection. Thus, at convergence plane 34, the beam is bent away from the aXis to such an extent that it follows, the path DH, exaggerated for emphasis, to deflection plane 35. Similar treatment of the other two beams in actual color tubes results in cross-over points of the three beams being at the. apertures of the, mask at all positions.

Point E in deflection plane 35 is the point which corresponds to that occupied by a light source when the phosphor dots. were located photographically on phosphor screen 32 through aperture mask 33. Therefore, a straight line. drawn from B through B in aperture mask 33. would intersect phosphor screen 32 at. point I which would be the center of the phosphor dot on which it is desired that the beam from gun 31 impinge. Unfortunately, however, in the. attempt to preserve all beam cross-over points at aperture mask 33, the beam no longer passes through deflection plane 35 at point E but passes through at point H. A straight line which approximates beam path drawn from point H through B, in the aperture mask 33 intersects the phosphor screen 32 at point C.

Bending of the beam at convergence plane 34 causes passage of the beam through point H of the deflection plane 35. This displacement EH is related to. the beam shift C] on phosphor screen 32 approximately by the ratio BC/EB, that is EH= (EB/BC)CJ.

Perhaps the simplest method of measuring the magnitude of the beam shift in a completed tube is to converge the beams by static converging forces in the extreme corners of the tube. When the beams are returned to the central portion of the screen, the separation FG of a beam from the common axis at the tube axis multiplied by DE/DF gives the displacement EH.

Referring now to FIG. 3, a first solution to the problem of beam shift is illustrated. If, instead of a single convergence plane, two such planes are employed, the displacement EH as seen in FIG. 2. can be eliminated. FIG. 3 is so set up that it illustrates a plane taken through the tube axis as well as through the center of any given gun. Thus, an undeflected beam emanating from gun 31 passes through point D of the first convergence plane 34, through point E of deflection plane 35, through an aperture of mask 33 lying on the tube axis to screen 32. A deflected and converged beam from gun 31 passes to point D in first convergence plane 34, where it is bent inwardly and passes to point K of the second convergence plane 43 where it is bent outwardly to point E of the deflection plane 35. These beam paths are also greatly exaggerated for emphasis.

As may be seen from the drawing, the beam is bent inwardly toward the tube axis at convergence plane 34 screen) as opposed to the outward bending applied in the prior art as shown in FIG. 2. At convergence plane 43, the bending action is reversed and the beam is bent away from the axis to such an extent that it follows a path which is actually still converging on, but almost parallel to, the tube axis to point E of the deflection plane 35.

Each of the three beams could be similarly illustrated in a plane including the proper gun and the tube axis. The result is that the three beams converge at each aperture of the mask 33 and are centered on the phosphor dots of screen 32, whether at the center or edges of the screen. The underlying reason for this result is, of course, the fact that point E of deflection plane 35 closely approximates a point corresponding to the location of the light source which originally fixed the location of the phosphor dots through mask 33.

Referring now to FIG. 4, one practical structure for accomplishing objects of the present invention is shown. For purposes of clarity, the structure illustrated is a portion of that which would be used with only one electron gun. The working device actually includes three such structures, one for each electron beam. However, the structures are identical and showing all would confuse rather than aid understanding.

In tube 51, there are disposed at set of soft iron pole pieces 52 which cooperate with an electromagnet 53 external to tube 51 to provide the converging forces indicated in FIG. 3 as the first convergence plane 34. Similarly, a second set of pole pieces 54 cooperate with an electromagnet 55 to form the second convergence plane 43 of FIG. 3. Supporting rods of non-magnetic material or other conventional means (not shown) support pole pieces 52 and 54.

The turns on the coil of electromagnet 53 are wound in series opposition to, and should be somewhat less in number than, those of the coil of electromagnet 55. In the specific case of the 22 rectangular screen color tube a turns ratio of 111.2 between electromagnets S3 and 55 has been satisfactory. Since the turns ratio for satisfactory beam bending will vary with many factors including tube size, operating voltages, configuration of magnetic components and the like, this example should not be construed in a limiting sense. A parabolic current wave such as conventionally used for dynamic convergence is applied to the terminals of the electromagnets. This is preferably derived from the deflection yoke.

Referring now to H6. 5, there is illustrated a second and compromise solution to the problem of degraded color purity caused by beam shift under dynamic conergence. In the manufacture of aperture mask color tubes, as previously noted, the location of the phosphor dots has been established by light sources disposed at points corresponding to the apparent sources of electrons in a completed tube. Again as noted, the use of dynamic convergence has resulted in an undesirable beam shift at or near the screen edges, because the dynamically converged beams fail to pass through the apparent source points in the deflection plane thus causing a beam dot misregister at the screen edges wherein the beams land radially outwardly of their on-center position when measured relative to a tri-color phosphor dot triangle. This is illustrated in FIG. 1 wherein the beams 25, 2s and 27 at the edges of the screen 12 are shown with a maximum misregister (which might, in some cases move the beams completely oft their respective phosphor dots) while the beams in, 17 and 125 at the center of the screen 12 are properly in register with their respective screen areas or dots 13, 14 and 1d. Apparatus has been shown and described which accomplishes the objective of passing the beams through the apparent source points, but the problem may be resolved in an alternative manner in the fab rication of the tube.

In the prior art process, panel 61 would be the base on which the phosphor dots of the screen are to be formed and mask 62 the mask to be used in the completed tube.

Light from a point source 63 would then be used to form phosphor dot as at the screen edge and phosphor dot 65 at the screen center.

If, however, a new location 63A spaced radially outward, with respect to the tube axis, from source 63 is used as the source, phosphor dots can and 65A will be formed at points displaced from dots M and 65 on panel 51. The same procedure can be repeated with each light source. That is, each li ht source is moved radially outward with respect to the tube axis from the normal positions used in tube fabrication, as taught, for example, in the above-cited application of Perry and Rowe, thereby moving each phosphor dot of each phosphor dot triangle radially outward with respect to the center of its respective phosphor dot triangle.

A tube made in accordance with this teaching would when completed have one of its apparent sources of electrons located at point 63. Let it be considered that electron beams begin their travel with a converging angle which is mechanically predetermined by the tilt of the guns. in the undefiected case, there would be no change of beam path at the convergence plane, and the crossover point of the beams would be at the aperture mask. Each beam would then no longer be centered on the phosphor dots of the dot triangle at the center of the screen area on which it is designed to impinge because of the outward shift of the phosphor dots as described above. The eccentricity will not be excessive, however. In fact, the shift of beam landing point is almost indiscernible in the center and has no effect whatsoever on purity.

At the edge areas of the screen, a different situation exists. A full deflection with maximum dynamic convergence being employed, the mechanically set converging angle of the beams is modified considerably, and the beams are bent outwardly with respect to the center of the beam triangle from their original course. The beams continue on their path of decreased convergence and pass through the deflection plane at points very nearly approximating points which would be determined by straigat lines drawn from the centers of peripheral phosphor dots, through the appropriate aperture, and intersecting the deflection plane.

in other words, the beams are centered at points which are radially outward with respect to the centers of the phosphor dot triangles of the central points of phosphor dots that would be found if those phosphor dots were disposed in accordance with the prior art. However, because the light sources have been moved radially outward with respect to the tube axis in fabricating the tube in accordance with the present invention, the phosphor dots are similarly displaced outwardly with respect to their respective phosphor clot triangles and the points of imingemcnt of the are more nearly concentric with the phosphor dots.

The present invention therefore :finds advantageous use in multiple-beam color-kincscopes wherein the multiple electron-bearns are subjected to dynamic convergence in scanning a screen unit of the kind including a mask containing a pattern of equally spaced dot-like apertures through which electrons, derived from said beams, pass in substantially straight line paths and impinge on preselected, dot-like, color-phosphor screen-arcas. T he electrons passing through the mash are in the form of elec tron-jets of a diameter smaller than the diameter of the electron-beams since the mask apertures are effective, as is known in the art, to neck down the beams as they pass thereth-rough. The pro-selected, dot-like, color-phosphor screen-areas on which the electrons land are arranged in a pattern, known to the art, which is systematically related to the pattern of apertures in the mask. The improvement provided by the present invention comprises a systematic relationship of the spacing and arrangement of the aforementioned dot-like patterns wherein the distance between the centers of those screen areas which lie adjacent to the central region of the screen-pattern is greater than the distance between the centers of the straight jet-paths which terminate on the screen. In the present illustrative embodiment this relationship may be appreciated by considering the relationship of a triangle of electron beams landing at the center of the screen and a triangle of phosphor dots laid down in accordance with the teachings herein. This relationship for the prior art is shown in FIG. 1 where it is seen that the distance between the centers of the beams 16, 17, 18 is the same as the distance between the centers of the dots l3, l4, 15 at the center of the screen. When a screen-pattern is constructed as taught herein, this relationship is changed. By moving the light sources radially outward, as shown in FIG. 5, the dots in a given phosphor dot triangle are moved outwardly with respect to that triangle. This will somewhat increase the spacing between the screen-areas or dots such that the distance between the screen areas at the center of the screen will be greater than the distance between the paths of the electron beams.

By fabricating tubes in the manner described immediately above, the area of maximum available tolerance, namely, the center screen area is allowed to be less precise. This procedure enables correction and greater precision in areas of minimum tolerance, namely the screen edge areas. The sacrifice is eminently justified, however, because improvement of edge purity is accomplished without the slightest discernible deterioration of center purity.

Although specific embodiments of the present invention have been shown and described in some detail, the invention should not be limited to the details shown. The concept of improving edge purity by compensating for errors introduced by prior art dynamic convergence is believed to be novel and essential to the present invention which should be limited only by the spirit and scope of the appended claims.

The invention claimed is:

1. Color television apparatus comprising, a color television picture tube of the dot screen, apertured shadow mask type having a plurality of electron guns, :1 first convergence electromagnet for increasing the angle at which beams from said guns converge on the axis of said tube, a second convergence electromagnet for decreasing the angle at which beams from said guns converge on the axis of said tube, and a deflection yoke for scanning said beams entirely over said shadow mask.

2. Color television apparatus comprising, a color television picture tube of the dot screen, apertured shadow mask type having a plurality of electron guns, a first convergence electromagnet for increasing the angle at which beams from said guns converge on the axis of said tube, a second convergence electromagn'ct for decreasing the angle at which beams from said guns converge on the axis of said tube, and a deflection yoke, said beams passing through said deflection yoke at points lying on extensions of straight lines determined by the centers of the dots on said screen and the centers of the apertures of said shadow mask.

3. Color television picture-reproducing apparatus comprising, a cathode ray tube including a luminescent screen, a shadow mask and a plurality of electron beams, a first system for converging said beams within said tube, a second system for diverging said beams within said tube, a third system for simultaneously deflecting all of said electron beams to scan substantially over said luminescent screen, and means for controlling the covergence of said beams by said first system as a function of the output of said third system to cause said beams substantially to converge at each aperture of said shadow mask after passing through a predetermined point within said third system.

4. A color television picture tube having a plurality of electron beams therein and means for controlling and directing said electron beams, said means including a like plurality of electron guns, a dynamic convergence system, a deflection system, a shadow mask having a multiplicity of equally spaced apertures formed therethrough and a luminescent screen consisting of a mosaic of phosphor dots, the spacing of the centers of the individual phosphor dots of said mosaic being graduated from a minimum at the central portion thereof to a maximum at the outer edges thereof sequentially disposed along said tube, separate ones of each of said electron beams emanating from a separate one of said electron guns, passing through separate predetermined points in said dynamic convergence system and said deflection system and simultaneously through the same aperture in said shadow mask and impinging on adjacent phosphor dots on saidluminescent screen, the angles between said electron beams being variable in accordance with the angle of deflection of said electron beams and having a predetermined magnitude when said angle of deflection equals one half its maximum value to cause said electron beams to be in substantially perfect registration with the phosphor dots of said mosaic at such angle of deflection.

5. Color television apparatus for a color television picture tube having a shadow mask, three electron guns and three electron beams directed from said electron guns toward said shadow mask, comprising the combination of a first and a second set of convergence electromagnets and adeflection yoke sequentially disposed along said tube, separate ones of each of first and second set of convergence electromagnets being further disposed to coact with each of said electron beams, said first set of convergence magnets being disposed to increase the angle at which each said beam converges on the axis of said tube, said second set of convergence electromagnets being disposed to decrease the angle at which each of the said beams converge on the axis of said tube, said deflection yoke being disposed to scan each of the said beams entirely over said shadow mask and means for energizing said first and said second set of electromagnets from said deflection yoke.

6. Color television apparatus comprising in combination an envelope, a set of convergence electromagnets and deflection means, said envelope having a luminescent screen deposited adjacent the viewing end thereof, said luminescent screen consisting of a mosaic of similarly sized phosphor dots, the spacing between the centers of individual ones of said phosphor dots being a minimum in the central portion of said mosaic and increasing to a maximum at the edge of said mosaic, said set of convergence electromagnets and said deflection means being disposed about said envelope adjacent said electron gun, means for directing the electron beam from each of said electron guns toward adjacent ones of said phosphor dots through said set of convergence electromagnets and said deflection means, and means for separately energizing said set of convergence electromagnets and said deflection means whereby said electron beams are centered on said phosphor dots when said electron beams are deflected to an angle equal substantially to one-half the maximum angle of deflection.

7. In a multiple-beam color-kinescope wherein the multiple electron-beams are subjected to dynamic convergence in scanning a screen-unit of the kind comprising a mask containing a pattern of equally spaced dotlike apertures through which electrons, derived from said beams, pass in transit along substantially straight paths to pre-selected, dot-like, color-phosphor, screenareas arranged in a pattern which is systematically related to said first mentioned pattern; the improvement which comprises: a systematic relationship of the spacing and arrangement of said dot-like patterns wherein the distance between the centers of those screen-areas which lie adjacent to the central region of said screen-pattern is greater than the distance between the centers of the straight paths which terminate thereon.

8. In a multiple-beam color-kinescope wherein the multiple electron-beams are subjected to dynamic convergence in scanning a screen unit of the kind comprising a mask containing a pattern of equally spaced dot-like apertures through which electrons, derived from said beams, pass in the form or electron-jets of a diameter smaller than that of said beams in their transit along substantially straight paths to pro-selected, dot-like, coiorphosphor, screen-areas arranged in a pattern which is systematically related to said first mentioned pattern, the improvement which comprises: a systematic relationship of the spacing and arrangement of said dot-like patterns wherein the distance between the centers of those screenareas which lie adjacent to the central region of said screen-pattern is greater than the distance between the centers of the straight paths which terminate thereon and the distance between the centers of those screen-areas which lie in a region surrounding said central region of said screen pattern is less than the distance between the centers of the straight paths which terminate on said last-mentioned screen-areas.

9. The invention as set forth in claim 8 and wherein said last mentioned region of said screen-pattern comprises a marginal edge portion of said screen-pattern.

10. The invention as set forth in claim 9 and wherein the variation in the distance between the centers of said screen-areas and the centers of said straight paths is substantially uniform as measured outwardly from the center of said screen-pattern to the marginal edges thereof.

References Cited in the file of this patent Re. 23,838 Re. 23,964 2,590,764 2,595,548 2,625,734 2,646,521 2,646,529 2,679,614 2,710,890 2,727,828 2,734,013 2,742,522 2,752,520 2,757,301 2,769,110 2,855,529

UNITED STATES PATENTS Rajchman June 8, r Jenny Mar. 22, 1955 Forgue Mar. 25, 1952 Schroeder May 6, 1952 Law Ian. 20, 1953 Rajchman July 21, 1953 Werenfels et a1. July 21, 1953 Friend May 25, 1954 Skellett June 14, 1955 Law Dec. 20, 1955 Myers Feb. 7, 1956 Law Apr. 17, 1956 Morrell June 26, 1956 Jones et a1. July 31, 1956 Obert Oct. 30, 1956 Morrell Oct. 7, 1958 OTHER REFERENCES and A. M. Morrell, RCA Review,

vol 16, pp. 122-439,

March 1955. 

1. COLOR TELEVISION APPARATUS COMPRISING, A COLOR TELEVISION PICTURE TUBE OF THE DOT SCREEN, APERTURED SHADOW MASK TYPE HAVING A PLURALITY OF ELECTRON GUNS, A FIRST CONVERGENCE ELECTROMAGNET FOR INCREASING THE ANGLE AT WHICH BEAMS FROM SAID GUNS CONVERGE ON THE AXIS OF SAID TUBE, A SECOND CONVERGENCE ELECTROMAGNET FOR DECREASING THE ANGLE AT WHICH BEAMS FROM SAID GUNS CONVERGE ON THE AXIS OF SAID TUBE, AND A DEFLECTION YOKE FOR SCANNING SAID BEAMS ENTIRELY OVER SAID SHADOW MASK.
 7. IN A MULTIPLE-BEAM COLOR-KINESCOPE WHEREIN THE MULTIPLE ELECTRON-BEAMS ARE SUBJECTED TO DYNAMIC CONVERGENCE IN SCANNING A SCREEN-UNIT OF THE KIND COMPRISING A MASK CONTAINING A PATTERN OF EQUALLY SPACED DOTLIKE APERTURES THROUGH WHICH ELECTRONS, DERIVED FROM SAID BEAMS, PASS IN TRANSIT ALONG SUBSTANTIALLY STRAIGHT PATHS TO PRE-SELECTED, DOT-LIKE, COLOR-PHOSPHOR, SCREENAREAS ARRANGED IN A PATTERN WHICH IS SYSTEMATICALLY RELATED TO SAID FIRST MENTIONED PATTERN; THE IMPROVEMENT WHICH COMPRISES: A SYSTEMATIC RELATIONSHIP OF THE SPACING AND ARRANGEMENT OF SAID DOT-LIKE PATTERNS WHEREIN THE DISTANCE BETWEEN THE CENTERS OF THOSE SCREEN-AREAS WHICH LIE ADJACENT TO THE CENTRAL REGION OF SAID SCREEN-PATTERN IS GREATER THAN THE DISTANCE BETWEEN THE CENTERS OF THE STRAIGHT PATHS WHICH TERMINATE THEREON. 